Process incorporating sodium pyrophosphate treated kaolinite within polyester



United States Patent Qfiice 3,376,249 Patented Apr. 2, 1968 3,376,249 PROCESS INCORPURATING SODIUM PYRO- PHOSPHATE TREATED KAOLINITE WlTH- IN POLYESTER Richard Young Meelheim, Kinston, N.C., assignor to E. l. du Pont de Nemours and Company, Wilmington, DeL, a corporation of Delaware No Drawing. Filed Sept. 8, 1964, Ser. No. 395,019 Claims. (Cl. 260-40) This invention relates to improved textile products, such as yarns, filaments, and fibers, and to their preparation. More particularly, it relates to an improved method of preparing synthetic linear polyester compositions for spinning into textile fibers possessing novel luster and friction properties.

Conventional melt-spun polyester filaments have been characterized by a smooth surface which gives high yarn running friction, high static friction and high surface luster. Attempts have been made to reduce friction and luster by special sizing treatments, or other surface coatings, and by adding finely-divided inert materials to the polymer before spinning. Neither approach has been completely successful. For example, the addition of many finely-divided inert materials to the molten polymer leads to the plugging of filter-packs in the melt-spinning operation with a consequent reduction in efficiency of operation. On a commercial scale, any such reduction in efiiciency would be prohibitive. Furthermore, the presence of many inert materials leads to an excessive reduction in maximum yarn strength. Reduced luster has been attained by adding pigments such as titanium dioxide, but TiO also increases fiber opacity, which is frequently undesirable. Also, the conventional addition of TiO has not provided the desired reduction in friction.

The present invention provides an improved procedure for preparing synthetic polyester textile fibers having reduced surface luster. A further contribution is the provision of a method for preparing melt-spun polyester fibers exhibiting reduced running and static friction. Another advantage is that these improvements are accomplished by a procedure for incorporating an inert material in a polyester fiber without significant loss of strength in the fiber. A still further advantage is the provision of a procedure for incorporating a finely-divided inert material in a polyester fiber without encountering excessive plugging of spinneret filter-packs during melt-spinning.

In accordance with the presence invention a procedure is provided by which finely-divided inert pigment of the kaolinite crystal structure, composed of thin hexagonal platelets of Al O -2SiO -2H O and referred to hereinafter simply as kaolinite, can be incorporated in synthetic linear condensation polyester textile fibers to provide the above and other improvements disclosed herein. It has been found that a pre-combination of kaolinite with 0.1% to 0.9% by Weight of pyrophosphate, based on the weight of kaolinite, can be dispersed in glycol and added in the conventional polymerizing step for preparing the fiber-forming polyester. A polyester having an intrinsic viscosity of at least 0.3 is then prepared, melt-spun into filaments and drawn into textile fibers in conventional manner. The kaolinite must be finely divided, consisting of particles which have equivalent spherical diameters in the range of 0.2 to 7 microns with an (E.S.D.) value in the range of l to 5 microns, as defined subsequently. Preferably, the kaolinite is dispersed in glycol which is used as an ester-forming component in the polymerization step.

By this procedure, polyester fibers containing up to 10% by weight of kaolinite may be readily prepared. For most textile purposes, it is preferred that the fibers containfrom 0.25 to 3.0% by weight of kaolinite.

The above process produces a drawn synthetic linear condensation polyester fiber having randomly dispersed therein hexagonal platelets of kaolinite oriented roughly parallel to the fiber axis. Microscopic inspection reveals that each platelet is surrounded by an elongated void where the polymer has separated from the particle and that the fiber surface exhibits slight protrusions and hollows. The filaments show a subdued surface luster, but do not have the gross reduction in transparency characteristic of similar yarns containing equivalent amounts of TiO Standard friction tests indicate a marked reduction in both dynamic and static frictional properties. Fiber strength is substantially equal to that of otherwise similar fibers containing no kaolinite.

The fibers produced by the process of this invention show reduced and more uniform running tensions, with greatly improved performance in mill processing, i.e., spooling, twisting, quilling, and weaving. Fabric prepared from these fibers shows a more uniform fabric structure, fewer streaks or flashes and less barr.

Conventional titanium dioxide (TiO delustrant can also be used with the kaolinite in the above process to achieve a wide variety of combinations of surface luster and opacity. By proper choice of the kaolinite/Tio ratio, the polyester yarn manufacturer is now able to prepare yarns with subtle luster effects hitherto unobtainable in a commercial process.

Hexagonal platelets of aluminum silicate having the kaolinite crystal structure are described by C. E. Marshall in The Colloid Chemistry of the Silicate Minerals, Academic Press, Inc., New York, N.Y. (1949), pp. 49 and 72. For the purposes of this invention, it is necessary to use a highly purified kaolinite which is substantially free of oxides of metals other than aluminum and silicon. It is further necessary to use a kaolinite in which the particles have equivalent spherical diameters in the range 0.2 to 7 microns and an (E.S.D.) value in the range 1 to 5 microns. The term equivalent spherical diameter refers to the diameter of a sphere having the same volume as the kaolinite particle, and may be calculated from measurements made on electronmicrographs of particles or from conventional sedimentation measurements. The (E.S.D.) 5g value is that equivalent spherical diameter which is exceeded in size by just 10% by weight of the particles measured. -(E.S. D.) Y, is specified in preference to average particle size since it gives better control of that portion of the kaolinite sample having the larger particle size range. This is important because the larger particles have the greater effect upon surface toughening, plugging of filter-packs, and yarn strength loss.

The presence of even small quantities of particles larger than about 7 microns not only results in an appreciable drop in maximum fiber tenacity but also produces plugging of filter-packs in the melt-spinning operation. On the other hand, particles smaller than about 0.2 micron do not provide sufficient toughening effect to filament surfaces for reduced running tensions.

The tetrasodium. pyrophosphate apparently serves as a deflocculating agent, both in the glycol slurry and in the molten polyester. In carrying out the process of this invention it is essential that the kaolinite particles 'be combined with tetrasodium pyrophosphate before being suspended in glycol. All procedures in which kaolinite and V the pyrophosphate are added to glycol separately have resulted in failure. Furthermore, dry powder mixtures of kaolinite and tetrasodium pyrophosphate, prepared by combining and stirring or grinding together the two materials in a dry state, are not operable in the process of this invention.

A suitable combination of kaolinite and pyrophosphate is prepared by mixing the two materials in an aqueous medium and then removing the water, e.g., by spray drying. In this manner an intimate precombination is assured, presumably with the surface of each particle of kaolinite being coated with tetrasodium pyrophosphate particles of near-molecular size. As indicated previously, it is preferred that the weight of tetrasodium pyrophosphate present in the mixture be equal to 0.1 to 0.9% of the weight of kaolinite.

Precombination of kaolinite with pyrophosphate may be conveniently accomplished in the conventional process used to prepare sized and graded kaolinite for commercial markets. For example, kaolin may be mined, washed, ground and pulverized, then suspended in an aqueous solution of sodium silicate for fractionation by settling. The settled material in the fraction of desired particle size is then redispersed in water containing an appropriate amount of tetrasodium pyrophosphate and spray dried. This product, without further treatment, is ready for immediate suspension in glycol and addition to a polyester polymerization system. No additional defiocculants need be added. Kaolinite slurry concentrations up to about 50% are useful.

The precombination of pyrophosphate-treated kaolinite is particularly suitable for use in situations where both titanium dioxide and kaolinite particles are added to the same polymerization system. Agglomeration is particularly troublesome when TiO is used with kaolinite, especially when added in the same slurry, unless the kaolinite has been pretreated with pyrophosphate deflocculating agent.

The kaolinite slurry is incorporated in the polymer by adding it to the polyester-forming reactants at the beginning of the polymerization, or at some later point during the polymerization procedure. Preferably, the slurry is added after polymerization has started, but before an appreciable viscosity change has been realized. In the ester interchangepolymerization procedure of Whinfield and Dickson, US. Patent No. 2,465,319, it is preferred that the glycol slurry be added after ester interchange has been completed but before the intrinsic viscosity level of the polymer has reached 0.1.

Following addition of the slurry to the polymerization mixture, the process is carried out in the conventional manner to give a fiber-forming high polymer. The polymer formed maybe forwarded in the molten state through conduits to a spinning machine to be melt-spun into filaments which are subeequently drawn to give strong textile fibers. Alternatively, the polymer may be extruded as a ribbon, quenched, cut to flake and subsequently remelted for spinning into textile fibers on conventional melt-spinning equipment. The amount of kaolinite used can be adjusted by the yarn manufacturer to impart a variety of good yarn luster and frictional properties.

The term synthetic linear condensation polyester, as used herein, comprehends a substantially linear polymer of fiber-forming molecular weight comprising a series of predominantly hydrocarbon groups joined by a recurring carbonyloxy radical, e.g., a polyester from glycol and dibasic acid components which is represented Iby the general formula,

As used herein, the term polyester is intended to include homopolyesters, copolyesters and terpolyesters prepared from bifunctional components. Included, for example, are the polyesters disclosed in U.S. Patents Nos. 2,465,319, 2,901,466 and 3,018,272. Polyesters having an intrinsic viscosity of at least about 0.3 are considered to be of fiber-forming molecular weight. Intrinsic viscosity has been defined in US. Patent No. 3,057,827.

Dibasic acid components useful in the preparation of polyesters and copolyesters of this invention include 4 terephthalic acid, isophthalic acid, sebacic acid, bibenzoic acid, hexahydroterephthalic acid, ethylenedibenzoic acid, isopropylidinedibenzoic acid, 4,4 dicarboxydiphenyl ether, 4,4"-dicarboxy-m-terphenyl, 2,6- and 2,7-naphthalenedicarboxylic acid. Glycol components useful in the preparation of the polyesters and copolyesters of this invention include the polyrnethylene glycols such as ethylene glycol and tetramethylene glycol and branched chain glycols such as 2,2-dimethyl-1,3-propanediol and 2,2- dimethyl-1,4-butanediol. Also included are cisand trans-hexahydro-p-xylylene glycol, bis-p-(2 hydroxyethyl)'benzene, diethylene glycol, bis-p(beta-hydroxyethoxylbenzene, bis-4,4-(beta-hydroxyethoxy)diphenyl, 1,4- dihydroxy [2 2 2] bicyclooctane, 2,2-bis (4-hydroxyphenyl)propane, 2,2-bis(4-hydroxycyclohexyl) propane, cyclohexanediol, 4,4'-dihydroxybiphenyl, and (bicyclehexyl)-4,4'-dimethanol. Other polyester-forming reagents include such bifunctional components as beta-hydroxypivalic acid, hydroxyacetic acid, and the like.

The following examples illustrate the invention. They are not intended to limit it in any way.

Example 1 To 800 parts of ethylene glycol is added 200 parts of vide an average particle size of 0.55 micron, with an of 1.6 microns as determined by sedimentation measurements. The mixture is subjected to high speed stirring in a Waring Blendor before using.

Kaolinite-modified polyethylene terephthalate is prepared by introducing into a reaction vessel 1200 parts of dimethyl terephthalate, 800 parts of ethylene glycol, 0.6 part of manganous acetate, oxide. The mixture is heated at atmospheric pressure and methanol removed by distillation until no additional methanol is evolved, the final temperature being about 240 C. The reaction mixture is then transferred to an autoclave, together with 0.8 part of phosphoric acid, 2 parts sodium acetate, and a sufficient quantity of the above-prepared glycol slurry of kaolinite to give the. kaolinite concentration shown in the table. The temperature of the mixture 1 is raised to 275 C. and thepressure in the vessel reduced to 0.2 millimeter of mercury while the mixture isagitated by a stirrer. Heating is continued and glycol vapor removed continuously as the polymer viscosity increases to the desired level, whereuponthe polymer is extruded from the bottom of the autoclave as a ribobn, quenched in water and cut to flake. Even at the higher concentration of kaolinite, the flake shows no delustering effect.

After drying, the flake is remelted in a screw extruder and supplied to a spinning position having a conventional arrangement of sand pack and spinneret. The molten polymer is extruded through'a 34-hole spinneret, quenched in air, and subsequently drawn 2.987X at C. by the process of Heighton, US. Patent No. 3,101,990 to give a 70-denier (7. 8 tex) yarn having a break elongation of approximately 25%. Close examination of the drawn filaments reveals that the kaolinite particles are randomly dispersed throughout the polymer and oriented roughly parallel to the fiber axis. Each particle is surrounded by an elongated void which scatters light and reduces the transparency of the filament. The filament surface is char- 7 acterized by numerous bumps and hollows.

Monitoring of the pressure above the sand pack during spinning than that normally encountered with TiO at the same concentration level.

The coefficient of friction of filaments taken from each yarn is measured according to the procedure described below with the results recorded in the following table. The

and 0.9 part of antimony trireveals that the pressure build-up is no greater TABLE Yarn Properties Coefficient of Polymer Analysis as in Example 1, and extruded through a 52-hole spinneret without noticeable filter-pack plugging. The filaments are Code Kaolinite, v

Percent Carboxyl Ether Tenacity, Friction (f Groups* Groups. g.p.d.

Percent Film Flooded 1A 0.00 21.0 2. 3. 71 0. 92 0. 92 1B 0. 37 17.9 2. 9 3. 66 0. 44 0.70 1C 0. 98 20. 3 2. 2 3. 08 0. 32 0.60 1D 1.48 15. 6 2. 1 3. 60 0.28 0. 56

* Expressed as equivalents/10" grams.

The coefficient of hydrodynamic friction, f is measured by hanging a test filament over a /2-inch diameter (12.7 mm. diameter) polished chrome-plated mandrel so that the filament contacts the mandrel over an arc of approximately 180. A 0.3-gram weight is attached to one end of the filaments (input tension) and a strain gauge is attached to the other end (output tension). The mandrel is rotated at a speed of 1800 rpm. and the area of contact fiooded with a drop of No. 50 mineral oil immediately before the strain gauge readings are made for the data marked flooded. For data marked film, the oil is wiped from the mandrel with only a thin film remaining. The coefficient, f,, is calculated from the belt equation:

1 T fr 5 In 1) where f is the coefiicient of hydrodynamic friction, In is the natural logarithm (log T is the input tension, T is the output tension, and a is the angle of wrap.

Yarns prepared as described above are cut into 3 inch staple .(89 mm. staple) and processed separately into spun yarn on the cotton system. The processability of the yarns containing the kaolinite particles is markedly better than that of the control yarn, showing reduced running tension, improved draftability, reduced roll wrapping, and the like.

In contrast with the above, unsatisfactory results are obtained when a commercially available kaolinite powder, having substantially the same particle size distribution as that in Example 1 but not coated with tetrasodium pyrophosphate, is stirred into glycol and incorporated in polyethylene terepht'halate by the general procedure described in Example 1. The glycol slurry of uncoated kaolinite powder and a glycol slurry of TiO can be used to produce a polymer which contains 0.3% TiO and 1.75% kaolinite, but when an attempt is made to melt-spin the polymer into a 70 denier (7.8 tex), 34 filament yarn an excessive build-up of pressure above the spinning-machine filter-pack will be encountered, necessitating shut-down of the machine after a short period of time. However, the use of a pyrophosphate-coated kaolinite, in accordance with the present invention, gives a negligible increase in pack pressure.

Example 2 A stream of monomeric bis(2-hydroxyethyl)terephthalate containing two mole percent of sodium 3,5-di(carbomethoxy)benzenesulfonate for dyeabi'lity, prepared by the method of Vodonik (U.S. Patent No. 2,829,153) and containing 0.02 weight percent antimony trioxide as a catalyst, is fed to a continuous polymerization apparatus. Also supplied to the system is a 20% glycol slurry of kaolinite powder coated with 0.3% by weight of tetrasodium pyrophosphate as described in Example 1. Sufficient kaolinite is added to give a concentration of 2% by weight in the final polymer. The temperature of the mixture is increased and the pressure reduced as it flows through a series of vessels with evolution of glycol, the final temperature being 275 C. and the final pressure being 1 millimeter of mercury in a vessel similar to that described by Pierce et al. in U.S. Patent No. 3,057,702. The finished polymer is forwarded in a molten condition to a spinning position,

quenched in cross-flow air and then drawn 2.91 X at C. with apparatus disclosed in Dusenberry U.S. Patent No. 3,045,315 to give a 70 denier (7.8 tex) yarn having a tenacity of 2. 42 g.p.d. and a break elongation of 16.6%.

Examination of the filaments shows a random dispersion of kaolinite particles, each associated with an elongated void where the polymer has pulled away from the particle during the drawing operation. The filament surface is characterized by numerous bumps and hollows which produce a subdued surface luster. The coefiicient of friction is measured according to the procedure in -Example 1 with the results shown below.

Coetficient of friction (f Film Flooded 0.63

The magnitude of the reduction in friction is more fully appreciated when it is realized that similar yarns containing no kaolinite particles usually give 1, values in the 0.80 to 1.00 range, as in sample 1A of Example 1.

The general procedure of Example 2 is repeated, but is modified by the addition of a 20% glycol slurry of TiO along with the kaolinite. Sufiicient TiO is added to give 0.3% by Weight in the final polymer. No problems are encountered with pigment flocculation or with excessive pressure build-up in the spinning machine filterpack.

The present invention provides a practical and efiicient process for preparing useful polyester fibers containing kaolinite particles. The prior art suggests neither the process nor the exceptional fiber properties obtained by adopting the improvement features disclosed and exemplified herein. The advantages of reduced surface luster and reduced friction, as well as the wide choice of luster effects obtained in combination with TiO may be achieved in a wide variety of polyester yarns including, for example, the non-round cross-sectioned fibers disclosed by Holland in U.S. Patents No. 2,939,201 and No. 2,939,202, the cotton-blending staple of Hebeler U.S. Patent No. 3,042,- 520, the high-bulk fibers of Kilian U.S. Patent No. 3,050,- 821, the interlaced continuous filament yarns of Bunting et al. U.S. Patent No. 2,985,995, the composite filaments of Jamieson U.S. Patent No. 2,980,492, the spontaneously extensible yarns of Kitson and Reese U.S. Patent No. 2,952,879, and the bulky yarns of Breen U.S. Patent No. 2,783,609. It is apparent that other variations and modifications of the disclosed procedures may be adopted without departing from the spirit of the present invention which is accordingly intended to be limited only by the scope of the appended claims.

I claim:

1. In the preparation of synthetic linear condensation polyester textile fibers, including the steps of polymerizing bifunctional ester-forming components to form a linear polyester having an intrinsic viscosity of at least 0.3, meltspinning the polyester into filaments and drawing the filaments into textile fibers; the improvement of treating finely-divided kaolinite with an aqueous solution of sodium pyrophosphate and removing the water to form a precombination of kaolinite with 0.1% to 0.9% by Weight of pyrophosphate based on the weight of kaolinite, dispersing said dry precombination in glycol and adding the dispersion in said polymerizing step to form a polyester containing up to 10% by weight of kaolinite based on the weight of polyester fibers; said kaolinite being substantially free of oxides of metals other than aluminum and silicon, and consisting of particles which have equivalent spherical diameters in the range of 0.2 to 7 microns with an (E.S.D.) value in the range of 1 to 5 microns.

2. The process defined in claim 1 wherein the glycol in which the kaolinite is dispersed is an ester-forming component in said polymerizing step.

3. The process defined in claim 1 wherein titanium dioxide delustrant is included in said polymerizing step in addition to the kaolinite to provide a combined effect on the surface luster and opacity of the textile fibers produced.

4. The process defined in claim 1 wherein the is a glycol terephthalate polymer.

5. The process defined in claim 1 wherein 0.25% to 3.0% by weight of kaolinite, based on the weight of polyester fibers, is incorporated in the polyester.

References Cited UNITED STATES PATENTS 1,438,588 12/1922 Feldenheimer 106-72 3,023,192 2/1962 Shivers 260-40 3,201,506 8/1965 Bills 260-40 3,221,226 11/1965 Kennedy et al. 260-40 3,318,718 5/1967 Beamesderfer et al. 106-72 MORRIS LIEBMAN, Primary Examiner.

polyester 15 R. S. BARON, Assistant Examiner. 

1. IN THE PREPARATION OF SYNTHETIC LINEAR CONDENSATION POLYESTER TEXTILE FIBERS, INCLUDING THE STEPS OF POLYMERIZING BIFUNCTIONAL ESTER-FORMING COMPONENTS TO FORM A LINEAR POLYESTER HAVING AN INTRINSIC VISCOSITY OF AT LEAST 0.3 MELTSPINNING THE POLYESTER INTO FILAMENTS AND DRAWING THE FILAMENTS INTO TEXTILE FIBERS; THE IMPROVEMENT OF TREATING FINELY-DIVIDED KAOLINITE WITH AN AQUEOUS SOLUTION OF SODIUM PYROPHOSPHATE AND REMOVING THE WATER TO FORM A PRECOMBINATION OF KAOLINITE WITH 0.1% TO 0.9% BY WEIGHT OF PYROPHOSPHATE BASED ON THE WEIGHT OF KAOLINITE, DISPERSING SAID DRY PRECOMBINATION IN GLYCOL AND ADDING THE DISPERSION IN SAID POLYMERIZING STEP TO FORM A POLYESTER CONTAINING UP TO 10% BY WEIGHT OF KAOLINITE BASED ON THE WEIGHT OF POLYESTER FIBERS; SAID KAOLINITE BEING SUBSTANTIALLY FREE OF OXIDES OF METALS OTHER THAN ALUMINUM AND SILICON, AND CONSISTING OF PARTICLES WHICH HAVE EQUIVALENT SPHERICAL DIAMETERS IN THE RANGE OF 0.2 TO 7 MICRONS WITH AN (E.S.D.) 10% VALUE IN THE RANGE OF 1 TO 5 MICRONS. 